High quality, convenient, cost-effective medical remote imaging has gained increasing importance during recent years. This is particularly true of imaging during surgical procedures, most importantly minimally invasive procedures in which direct viewing of the surgical field by the surgeon is difficult. For example, a method for performing coronary artery bypass relies on viewing the cardiac region through a thoracoscope or other viewing scope (see for example Sterman et al. U.S. Pat. No. 5,452,733 and Gifford, III et al. U.S. Pat. No. 5,695,504). By way of further example, a surgeon may need to perform a delicate vascular- or neuro-microsurgical reconstruction through a minimal incision with the aid of remote viewing. Minimally invasive surgical procedures and their related need for remote imaging are now common in orthopedics, ophthalmology, urology, gynecology, anesthesiology, and other medical disciplines.
In a conventional surgical environment, remote imaging is accomplished by attaching a video camera to an endoscope, laparoscope, or other minimally invasive instrument and transmitting the video image via cable to a conventional CRT video monitor. This is typically cumbersome in a crowded, brightly lighted operating room, where surgical team members are frequently moving about and the surgeon's view of the image screen is often obstructed. Additionally, the CRT monitor is incapable of providing the surgeon with critical depth perception, since it is not stereographic.
Head-mounted displays (HMDs) potentially offer a method for convenient medical remote viewing without obstruction of the image typical in an operating room environment. While head-mounted displays have been designed, developed and deployed in military applications for many years, such displays are generally bulky, expensive, application-specific devices that are not well suited to commercial or surgical applications.
With the advent of inexpensive and increasingly complex commercial computing power and computer graphic devices and software, there has been increasing interest and activity in the field of commercial HMD devices. A number of such devices are presently available, but because of the high cost of appropriate display components and the generally cumbersome mechanical nature of the headgear, these devices are generally low in resolution and unattractive for professional computing applications.
High-resolution display device components are now emerging, that can significantly enhance commercial HMDs and related applications. However, they require integration into an ergonomic, well engineered and economical design. In the case of professional and consumer computing applications, visual quality and comfort are critical to long-term acceptance. A computing environment generally includes the use of a keyboard as well as peripheral devices and supporting paperwork. Therefore peripheral vision is also an important consideration.
A compact HMD system requires a very small display device, such as those found in modern camcorder viewfinders, but with significantly higher resolution. A number of such devices are now becoming available, including transmissive and reflective liquid-crystal microdisplay devices and micro-mirror devices having resolutions at or in excess of VGA quality (640 pixels by 480 pixels) with pixel sizes on the order of 15 microns or less. Most of these devices exhibit satisfactory image contrast only when illuminated and viewed at narrow angles of incidence, which compromises field of view, eye relief, and viewing comfort.
Due to the base costs of their materials, such devices are expensive for commercial applications, even in high volumes. In particular, for stereographic or other binocular applications, the use of dual display devices for two eye channels results in a high cost. A medical stereographic HMD system having dual display devices is described in Heacock et al. "Viewing Ocular Tissues with A Stereoscopic Endoscope Coupled to a Head Mounted Display (HMD)," http://www.hitl.washington.edu/publications/heacock/, Feb. 17, 1998.
Kaiser Electro-Optics (2752 Loker Avenue West, Carlsbad, Calif. 92008 manufactures the "CardioView," "Series 8000," and "StereoSite" HMD display systems for Vista Medical Technologies. These systems are bulky, heavy, and expensive, and include two LCD display devices. For peripheral vision correction they require the user to wear the HMD over conventional corrective eyeglasses, aggrevating user inconvenience and discomfort.
Attempts to use only a single display device for such applications have typically involved beamsplitters, and have not achieved true stereographic performance (see for example Meyerhofer et al. U.S. Pat. No. 5,619,373, issued Apr. 8, 1997).
Therefore, what is needed in the art is a compact, high resolution, high contrast, truly stereographic system for microdisplay viewing, particularly for surgical microdisplay viewing, that is suitable for head-mounted display use without requiring undue complexity or expense. The system should provide good color fidelity for color image viewing, and should incorporate ergonomic design for comfort and efficiency, including peripheral vision accommodation and minimal cabling.